1. Field of the Invention
The present invention relates to a projector device adapted to guide light from a light source to an optical system to generate image light for magnification projection on a forward screen.
2. Description of Related Art
Conventionally known as a projector device of this type is a liquid crystal projector device adapted to separate white light emitted from a light source into three primary colors of blue, green, and red for incidence on three liquid crystal panels for three primary colors, to synthesize the light transmitted by the liquid crystal panels with a color synthesis prism to generate a color image, and to magnifyingly project the color image on a forward screen with a projection lens.
Known as one of those as described above is a liquid crystal projector device employing an integrator illumination optical system having, as shown in FIG. 48, two integrator lenses 210, 220 arranged between a light source 200 and a liquid crystal panel 290. The integrator illumination optical system includes the light source 200, first integrator lens 210, second integrator lens 220, a polarization beam splitter 230, and a field lens 240.
The integrator lenses 210, 220 are made of a fly-eye lens formed having a plurality of cells 211, 221, respectively, arranged in the form of a matrix, and have a function of uniformizing illuminance distribution across an imaging area of the liquid crystal panel 290. The polarization beam splitter 230 has a function of extracting only one component wave out of P- and S-waves of light, which allows the liquid crystal panel 290 to be irradiated with light polarized in the same direction.
As shown in FIG. 49(a) and FIG. 49(b), the polarization beam splitter 230 includes a polarizing plate 236 and a half-wavelength plate 233 with slits joined to a light emergence surface thereof. Inside the polarizing plate 236, first interfaces 232 for passing therethrough a P-wave of light incident on the polarizing plate 236 and reflecting an S-wave, and second interfaces 231 for reflecting the S-wave are alternately formed with an inclination angle of 45 degrees relative to the surface of the polarizing plate 236.
As shown in FIG. 49(b), the P-wave of the light incident on the first interfaces 232 passes through the first interfaces 232 to reach the half-wavelength plate 233. The P-wave has a phase thereof inversed by passing through the half-wavelength plate 233, and emerges as an S-wave. On the other hand, the S-wave reflected by the first interfaces 232 reaches the second interfaces 231, and is reflected by the second interfaces 231 to emerge from each slit 233a of the half-wavelength plate 233. Thus, only the S-waves emerge from the polarization beam splitter 230.
A slit plate 234 is placed at a light incidence side of the polarizing plate 236 because the polarization function of the polarization beam splitter 230 degrades if light is incident on the second interfaces 231 in the polarization beam splitter 230. The slit plate 234 has slits 234a located to allow light incidence on the first interfaces 232. The slit plate 234 prevents light incidence on the second interfaces 231. Therefore, in order to improve utilization efficiency of light from the light source 200, it is necessary to condense the light from the light source 200 toward the first interfaces 232 of the polarizing plate 236, that is, to the slits 234a of the slit plate 234.
Accordingly, in order to improve utilization efficiency of light from the light source, there has been proposed an integrator illumination optical system using, as shown in FIG. 50, two decentered integrator lenses 250, 260 with respective cells 251, 261 decentering optical axes in different directions (see JP 2000-194068, A). In the integrator illumination optical system, the cells 251, 261 constituting the two decentered integrator lenses 250, 260, respectively, have surfaces thereof formed with different curvatures depending on arrangement positions, such that the light from the light source 200 can be condensed to the slits 234a of the slit plate 234 shown in FIG. 49(b). This can enhance the light utilization efficiency.
The light is irradiated through the integrator illumination optical system on an irradiation area of the liquid crystal panel 290, which is set wider than an imaging area W of the liquid crystal panel 290 with a certain margin beyond the imaging area W.
However, the above integrator illumination optical system using the two decentered integrator lenses 250, 260 causes an acute step 270 to be formed at a border between a plurality of adjacent cells 251, 261 as shown in FIG. 51 because the cells 251, 261 have respective surfaces with different curvatures.
The acute step 270 as described is difficult to work, so that the step 270 easily exhibits obtuseness in the acute angle when the above decentered integrator lenses 250, 260 are worked. The obtuseness exhibited in the acute angle of the step 270 would produce a shadow in the periphery of a projection image. Therefore, it is necessary to use the two decentered integrator lenses 250, 260 without any obtuseness in the acute angle of the step 270.
The working of the decentered integrator lenses 250, 260 as described not only needs a high working technique, but also requires a high working accuracy. This has led to a poor yield, and made both decentered integrator lenses 250, 260 expensive, entailing a problem of increased production costs.
If the obtuseness in the step 270 of both decentered integrator lenses 250, 260 is allowed to some extent for cost reduction, in order to prevent a shadow from being produced in the periphery of a projection image, it is necessary to set a larger margin of the irradiation area for the light to irradiate the liquid crystal panel 290 beyond the imaging area W of the liquid crystal panel 290 than the conventional one. This has resulted in a problem in that the light utilization efficiency cannot be improved although the illumination optical system is constructed using the two decentered integrator lenses 250, 260.